Discovery of benzo[d]oxazole derivatives as the potent type-I FLT3-ITD inhibitors.

Fms-like tyrosine kinase 3 (FLT3) has been considered as a potential drug target for the treatment of acute myeloid leukemia (AML), because of its high and aberrant expression in AML patients, especially the patients with FLT3-ITD mutation. Initiating from a hit compound (IC: 500 nM against FLT3-ITD), a series of compounds were designed and synthesized based on benzo[d]oxazole-2-amine scaffold to discover new potent FLT3-ITD inhibitors. During the medicinal chemistry works, flexible molecular docking was used to provide design rationale and study the binding modes of the target compounds. Through the mixed SAR exploration based on the enzymatic and cellular activities, compound T24 was identified with potent FLT3-ITD inhibitory (IC: 0.41 nM) and anti-proliferative (IC: 0.037 μM against MV4-11 cells) activities. And the binding mode of T24 with "DFG-in" FLT3 was simulated by a 20-ns molecular dynamics run, providing some insights into further medicinal chemistry efforts toward novel FLT3 inhibitors in AML therapy.